With all the concerns surrounding seafood, buying fish has become a navigational nightmare. But don't let fear or confusion scare you away. Before heading to the market, learn a few simple rules.

Befriend a FishmongerBy developing a rapport with the person selling your fish, you'll feel comfortable asking important questions, and you'll get trustworthy information. If your seller doesn't know the answers, find another retailer.

Remember that because a store is small doesn't mean it's better. Many independent fish markets sell safe, sustainable seafood, but some may not. Meanwhile, larger chains may have stringent safeguards in place -- and the clout to enforce them. Whole Foods, for instance, visits its suppliers and producers worldwide to see how they operate. The company also prohibits fish farmers from using antibiotics and growth hormones, and requires that they "minimize the impacts of fish farming on the environment by protecting sensitive habitats," according to Carrie Brownstein, the company's seafood quality standards coordinator.

Regardless of where you shop, let your vendor know that you won't eat overfished species. Tom McCann, spokesman for Ocean Conservancy, says doing this gets the message across: "Educated consumers can put pressure on stores and restaurants so that everyone makes better decisions."

Buy WildWild fish typically are a sustainable, safe option. The naturally occurring nutrients they feed on often make for better taste. Plus, properly managed fisheries use methods that protect the ocean floor and the fish supply.

Look for the blue-and-white logo from the Marine Stewardship Council (on packaging, labels, and fish counter seafood tags), which certifies commercial fisheries that keep populations within sustainable levels, minimize environmental impact, and meet all local, national, and international laws of sustainability. You'll find the logo on wild Alaskan salmon, Oregon pink shrimp, and U.S. North Pacific sablefish (also known as black cod).

Note, though, that mismanaged wild fisheries do exist, depleting fish populations and damaging the ocean floor. To get them on the straight and narrow, organizations like Ocean Conservancy help put responsible management plans in place. For example, because of the group's recent work, it now recommends red snapper from the Gulf of Mexico, long considered a bad eco option. Why the change? The Gulf's regional fishery council put a science-based catch limit (also called a limited access privilege program) in place for the season. This helps rebuild diminishing populations.

You'll also want to make sure your wild fish hasn't come from polluted waters. Wild salmon that comes from Washington state and Oregon, for instance, can have high levels of polychlorinated biphenyls, or PCBs, which are potential carcinogens.

Don't Discount All FarmedNot all farmed fish deserves a bad rap. Sure, some farms cause pollution, destroy natural coastal habitats, and deplete and threaten local wild species. But well-regulated farms manage their systems responsibly and pose fewer environmental risks. Domestic barramundi and rainbow trout make good picks, as do farmed mollusks such as oysters and mussels, which can actually clean the waters they're grown in.

Farmed shrimp and salmon, on the other hand, warrant more questions. Shrimp farms can wreak havoc on local habitats, as torn-down coastlines become farming sites that then pollute the land around them. Salmon farms (set up in net pens placed along the coastline) may allow harmful pollution to seep into surrounding waters. Farmers often feed these salmon food pellets made with a synthetic chemical to give the flesh an orange pigment (wild salmon's color comes from eating krill, tiny crustaceans).

Again, ask questions to find out if your retailer avoids unacceptable fish. Wegmans grocery chain worked with the Environmental Defense Fund to set its own standards (for instance, that fresh shrimp must come from farms that prohibit antibiotics).

Buy Domestic (Most of the Time)"While not perfect, the United States has the most regulated fisheries in the world," says Nancy Civetta of the Pew Environment Group. These rules, which cover population management and safe fishing practices, make buying domestic better than buying from a country like China, which has lenient policies and struggles with water pollution.

Of course, exceptions exist. A number of northern European fisheries (including North Eastern Sea Fisheries sea bass and North Sea herring) have been certified sustainable by the Marine Stewardship Council. So how do you know where your seafood comes from? The United States now requires that most wild and farm-raised seafood have country of origin labeling. Inaccuracies can occur, so when in doubt, ask your fishmonger.

Be Wary of "Organic" The USDA doesn't yet have a certification program for organic seafood. But you'll still find "organic" on some labels. Why? The federal government doesn't prohibit international producers from labeling seafood organic. (The exception is California, which bans misleading labeling.)That said, a few domestic shrimp farms have received USDA organic certification because they qualify as livestock, not aquaculture, farms. By farming inland, some farms have also improved practices by recycling water and diminishing their pollution.

Factor in Health Eating a variety of seafood generally supports good health. Many species contain high amounts of omega-3s, or "good" fatty acids, which are important for cardiovascular health and pre- and postnatal neurological development, among other benefits.

Consider the Risks While some fish contain these good fatty acids, they also may have high levels of omega-6s, or polyunsaturated fats that may increase inflammation and blood clotting -- so enjoy options like tilapia and catfish in moderation.

Meanwhile, mercury and PCBs pose the two biggest health threats for seafood eaters. Mercury targets the nervous system and kidneys and can damage children's brains; PCBs, when consumed continuously at low levels, may act as carcinogens and affect nervous system development. Longer-living, large predatory fish such as shark and bluefin tuna have high amounts of both mercury and PCBs, but toxins even pop up in smaller species such as grouper. Consume these species sparingly; pregnant women and children should avoid them altogether. Conveniently, most of these fish are also overfished, so by avoiding them you'll protect yourself and the waters.

The Fish ListStill confused? Stick with these fish. They're good for you and the ocean.